Pyrolysis furnace with new type radiant tubes arrangement and method of its operation and usage

ABSTRACT

The present invention provides a pyrolysis furnace with new type radiant tubes arrangement and method of its operation and usage. The first pass tubes and second pass tubes of radiant tubes of pyrolysis furnace according to the present invention are located at two parallel planes respectively, the projection of second pass tube of radiant tubes in each group is corresponding to the center location of projection connecting line of two first pass tubes adjacent therewith. The present invention can also employ top burners and bottom burners; the inlet of crossover section is located at middle-upper portion of radiant section wall. The present invention has the feature of uniform heat conduction, high effectiveness, flexible and simple operation and control, and small investment, it is suitable for cracking reaction of hydrocarbons feedstock.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a pyrolysis furnace and method of itsoperation and usage, specially relates to a pyrolysis furnace with newtype radiant tubes arrangement for high temperature cracking reaction ofHydrocarbons, and the method of its operation and usage.

[0003] 2. Description of the Prior Art

[0004] As is known to all, the pyrolysis reaction of Hydrocarbons ismain means for production of very important industrial raw materialssuch as ethylene, propylene, etc. Even a little improvement occurs inthis field, it can bring about giant economic and social benefits.Pyrolysis furnace is the main equipment for performing high temperaturecracking, therefore, nearly all chief Hydrocarbons and petro-chemicalcompanies of the world pay great attention to and not spare to make hugeamount of investment for modification of pyrolysis furnaces.

[0005] As is under stood to person skilled in the art that thestructure, and uniform heat receipt of radiant tubes are importantfactors affecting the cracking reaction result. The radiant section oftraditional vertical pyrolysis furnace in most cases employ single rowtubes to ensure uniform heat receipt of radiant tubes. There are alsosome companies, which for the purpose to obtain larger productivity ofsingle furnace under lower investment EMPLOY double row tubes, and forcombined feature of both arrangements, EMPLOY staggered row tubes.Abovementioned content is available from reference to <<The technologyof ethylene>>, by Chen Bing (Chemical industrial pub house, 1997, 1sted, chap. 4) <<The theory and technology of pyrolysis for theHydrocarbons chemistry>> by Zhou Ren-juin (chemical industrial pub.house, 1981, 1st ed, chap 6) and <<Technique of device for ethylene>> byWong Song-hang (Hydrocarbons chemical industrial pub. house, China,1994, 1st ed chap 6).

[0006] The radiant tubes employing single row arrangement in radiantsection receive double-wall radiation; they have the most uniform heatreceiving and best heat conducting effect. But the disadvantage is thatin same area the number of tubes capable to be arranged is minimum, theproductivity of specific area is low. Under this condition of single rowarrangement, in order to meet the requirement of magnification ofpyrolysis furnace, it needs to extend the length of every radiant tubesor the length of radiant section, an inexorable result is that we haveto greatly increase the height and length of radiant section and meetthe more severe requirement for uniform heat supply by burners inradiant section. At same time extremely long radiant tube makes theengineering problems complicated. Therefore, the use of single rowarrangement structure significantly limits the productivity of pyrolysisfurnace.

[0007] Although the use of double row of radiant tubes arrangement canincrease the productivity by 70%, but the mutual overlap between tubesof double row seriously affects heat conductivity of heater wall fromits radiation, this results in worse conductive effect from radiation,at the same time, non-uniform heat receipt of radiant tubes brings aboutdisadvantages to cracking selectivity, employ cycle, and lifetime ofradiant tubes.

[0008] Although the use of staggered row arrangement can partly increaseproductivity and uniformity of heat receipt, but in order to ensureuniformity of radiant conduction, the distance between adjacent radianttubes must be not lower than 1.8 times of outer diameter thereof, thespace saved within furnace chamber is limited. Besides, in order toavoid mutual cross-link of radiant tube bends in adjacent groups andmanifolds in lower portion of furnace chamber, we have to locate thebends of adjacent groups and manifolds at different heights or differentplanes, this leads to two by-effects: at one hand, the radiant tubeslocated at different heights, having different overall lengths invarious groups, thus retained time and severity of feedstock isdifferent in various groups, this makes certain limitation to theoptimization controlling. At the other hand, the bends and manifoldslocated at different planes gives significant affectation to stress ofall radiant tubes, which easy to cause deformation of radiant tubes.Moreover, this leads to complicated design of radiant tube bends,multiple types-kinds, bad interchangeability, high difficulty inmounting and increased investment.

[0009]FIG. 6 shows an arrangement of prior art of two pass branchedradiant tubes 7 with different diameters of type 2-1 in radiant section3, wherein the first pass and second pass tubes are located in a sameplane, this is a single row arrangement. It can be seen that althoughthe tubes uniformly receive heat, but not so many tubes are arranged inradiant section, the space utilization is not high, as well as thearrangement of tubes is not symmetrical and tube lengths are not thesame, this leads to different working condition of cracking process invarious tubes, and thus the cracking effect is affected.

[0010] In addition, high temperature condition of cracking reaction isachieved by heat supply from burners to radiant tubes in the radiantsection. In accordance with the mounting location in the radiantsection, the burners are divided into bottom burners, wall burners andtop burners.

[0011] In U.S. Pat. No. 4,361,478 the company LINDE discloses apyrolysis furnace entirely employing heat supply manner by means of wallburners. The pyrolysis furnace entirely employing heat supply manner bymeans of wall burners has the feature of uniform temperaturedistribution in furnace chamber, small width of furnace chamber, etc,but too much burners are located in whole pyrolysis furnace,distribution piping of fuel is complicated, investment is large, and theemploy and maintenance in practice is an expensive matter.

[0012] In U.S. Pat. No. 4,999,089 the Japanese company MITSUI disclosesa pyrolysis furnace entirely employing heat supply manner by means oftop burners. At this manner, the structure of radiant section isirregular, the form of fuel current in furnace chamber is complicated,more over, the heater wall at radiant section is tilted, under thecondition of high temperature employ, the isolation lining materials ofheater wall are easy to be broken-up in employ, it results in greatamount of repair. Besides since the outlet of fuel gas is located atbottom portion of radiant section, the high-powered extraction fan isneed to provided for back current of fuel gas in radiant section, suchfurnace has increased cost and energy consumption.

[0013] In U.S. Pat. No. 5,151,158 the company S & W describes apyrolysis furnace with entire heat supply from bottom burners, it whollyuse heat supply from bottom burners, it is advantageous in simpleemploy, and minimum amount of maintenance. But the requirement toburners is relative high, when the height of furnace chamber at radiantsection is higher, it is, necessary to have some burners of specialdesign to meet uniform temperature requirement in furnace chamber. Theseburners are complex in manufacture and expensive.

[0014] In U.S. Pat. No. 4,342,642 the company LUMMUS discloses apyrolysis furnace with bottom-wall combined heat supply manner, althoughthis kind of heat supply manner can obtain uniform temperature infurnace chamber by means of conventional bottom or wall burners, but theuse of wall burners is still needed, thus such problems, as complexityof distribution piping, large investment and high cost of employ andmaintenance, etc, are still present in.

[0015] Abovementioned pyrolysis furnace of prior art generallycomprising: a convection section, used for preheating the hydrocarbonsfeed stock; a radiant section, used for high temperature crackinghydrocarbons feedstock; and crossover section, connected between theconvection section and radiant section. A typical pyrolysis furnace withbottom burning manner is shown in FIG. 5, wherein bottom burners 8 andmultiple groups of radiant tubes 7 are arranged in radiant section 3;the convection section is located above the radiant section and axiallyshifted therewith, wherein multiple groups of convection tubes 1 arearranged; a crossover section 6 is passed horizontally from top portionof radiant section to connect with bottom portion of convection section.The above mentioned pyrolysis furnace of prior art has greater overallheight, it increases design and technology difficulty and results inlarger amount of capital expenditure at same time.

[0016] To Sum up, all the furnaces of prior art have their advantages,but also have many shortages and problems. Therefore, it is necessary toseek for a pyrolysis furnace of new type with excellent compositiveproperties, to overcome above described shortages.

SUMMARY OF THE INVENTION

[0017] The object of the present invention is to provide a pyrolysisfurnace with new type radiant tubes arrangement in radiant section,which has the feature of simple employ, excellent heat conduction, smallinvestment, easy maintenance, and flexible control.

[0018] In order to realize above object, the inventor has carried thougha great deal of careful investigation and found that employ of new typeradiant tubes arrangement design in radiant section, which never hasbeen used by others, is effective means to solve abovementionedproblems.

[0019] The present invention provides a pyrolysis furnace with new typeradiant tubes arrangement, the pyrolysis furnace comprising:

[0020] a) vertically arranged radiant section, in which burners andmultiple groups of radiant tubes are arranged for high temperaturecracking hydrocarbons feedstock;

[0021] b) vertically arranged convection section, located above theradiant section and axially shifted therewith, in said convectionsection multiple groups of convection tubes are arranged for preheatingthe hydrocarbons feedstock;

[0022] c) horizontally arranged crossover section, connected betweensaid radiant section and said convection section;

[0023] Characterized in that

[0024] said multiple groups radiant tubes are two pass tubes withdifferent diameters, the first pass tubes and second pass tubes arelocated at two parallel planes, more over, the projection of each secondpass tube is corresponding to the center line of projection connectingline of two first pass tubes, adjacent therewith, the structure of eachfirst pass and second pass tube is the same.

[0025] In order to resolve the problem of arrangement and uniform heatreceipt of radiant tubes, said radiant tubes may be two passnon-branched tubes with different diameters (type 1-1) or two passbranched tubes with different diameters (type 2-1, 4-1), wherein the twopass branched tubes with different diameters (type 2-1) are particularlypreferred. Wherein the pitch between two adjacent radiant tubes in saidsame plane is 1.8˜6.0 times of outer diameter of the radiant tubes,preferably, 1.8˜4.2 times, more preferably, 2.0˜2.8 times, the distancebetween the planes where said first pass tubes and second pass tubes arelocated is 100˜600 mm, preferably, 200˜500 mm, most preferably, 300˜400mm.

[0026] The pyrolysis furnace of this invention may also employ a newtype heat supply manner, wherein top burners and bottom burners aresimultaneously arranged in said radiant section, and said crossoversection is extended from middle-upper portion of radiant section wall,and connected to bottom portion of convection section.

[0027] A further object of present invention is to provide method andusage of high temperature cracking hydrocarbons feedstock by means ofsaid pyrolysis furnace, including: preheating hydrocarbons feedstock anddilution steam mixture, etc, in convection tubes by means of fuel gascame from radiant section; high temperature cracking preheatedhydrocarbons feedstock, wherein maintaining the heat supply ability ofbottom burners constant, regulating the heat supply ability of topburners within a small range to satisfy different temperaturerequirement for cracking different kinds of hydrocarbons feedstock.

BRIEF DESCRIPTION OF DRAWINGS

[0028] The present invention will be better understood throughdescribing in reference to the following drawings, in which:

[0029]FIG. 1 is a diagrammatic elevation view of a new type pyrolysisfurnace according to the present invention;

[0030]FIG. 2 is a top view of radiant section of pyrolysis furnaceaccording to the present invention, taking as an example, the radianttubes are type 2-1;

[0031]FIG. 3 is an elevation view of FIG. 2 wherein two groups ofradiant tubes are shown;

[0032]FIG. 4 is a side view of FIG. 2;

[0033]FIG. 5 is a diagrammatic view of a typical pyrolysis furnaceemploying bottom burners heat supply in the prior art;

[0034]FIG. 6 is a diagrammatic top view and elevation view of a singlerow arrangement of radiant tubes in a pyrolysis furnace in the priorart.

DETALLED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] As FIG. 1 shows, the new type pyrolysis furnace of this inventioncomprising radiant section 3; bottom burners 8, arranged in radiantsection 3; multiple groups of two pass non-branched tubes with differentdiameters 7 (type 1-1) or two pass branched tubes with differentdiameters 7 (type 2-1, 4-1), vertically arranged in radiant section;wherein, tubes with different diameters means that the first pass tubeand second pass tube in two pass tubes has different diameter, but twoor four first pass tubes in two pass tubes type 2-1, 4-1 should havesame diameter; convection section 2, shifted from radiant section 3;multiple groups of convection tubes 1, horizontally arranged inconvection section 2; crossover section 6, horizontally arranged betweenradian section 3 and convection section 2;

[0036] The feedstock for cracking is introduced from the convectiontubes 1 in convection section of furnace through the crossover tube 5 ofconvection tubes 1 into radiant tubes 7, then successively pass throughthe first pass tubes (1 tube, 2 tubes or 4 tubes) of radiant tubes 7,second pass tube (1 tube), at last pass from outlet of second pass tubeof radiant tubes 7 into Transfer Line Exchange(TLE) 4.

[0037] In order to resolve the problem of radiant tube construction,arrangement, and uniform heat receipt, said radiant tubes may be twopass non-branched tubes with different diameters (type 1-1) or two passbranched tubes with different diameters (type 2-1), wherein the two passbranched tubes with different diameters (type 2-1) are particularlypreferred.

[0038] The first pass tubes and second pass tubes of various groups arelocated at two parallel planes respectively, and the projection of eachsecond pass tubes is corresponding to the center location of projectionconnecting line of two first pass tubes, adjacent there with, and thestructure of each first tube and second tube is the same respectively,wherein the pitch between two adjacent radiant tubes in said same planeis 1.8˜6.0 times of outer diameter of the radiant tubes, preferably,1.8˜4.2 times, more preferably, 2.0˜2.8 times; the distance betweenfirst pass tubes and second pass tubes of each group is 100˜600 mm,preferably, 200˜500 mm, most preferably, 300˜400 mm.

[0039] Because the present invention employs new type arrangement ofradiant tubes, so as to make the pitch between two adjacent radianttubes in same plane to be just right, the bends of radiant tubes ofradiant section in various groups and manifold are parallel each otherwithout cross link, this has no influence on radiant heat conduction ofradiant tubes in various groups, simultaneously, the form and weight ofbends of radiant tubes in various groups and manifold are fully thesame, these components have high versatility, and are simple formanufacture and maintenance; the overall length of radiant tubes ofradiant section in various groups are fully the same, the residence timeand pressure drop of feedstock are fully the same, which is easy tooptimization of employ and control; the weight of radiant tubes ofradiant section in various groups is fully the same, this makes thebalance and suspension system easy to be arranged and regulated.

[0040] Because this arrangement can reduce the length of pyrolysisfurnace, it is suitable to various traditional or new type TLEs.

[0041] In pyrolysis furnace, according to the present invention, topburners 9 can also be added in radiant section, as shown in FIG. 1. Thelocation of the crossover section 6 can be determined by the top/bottomburners' heat supply ratio R of different pyrolysis furnaces. When Rvaries in a range of 1:9˜7:3, the top wall of crossover section islocated under the top wall of radiant section, its distance H is 10%˜50%of total height of radiant section wall, preferably, R varies in a rangeof 2:8˜6:4, H is 10%˜40% of total height of radiant section wall; morepreferably, R varies in a range of 2.5: 7.5˜5:5, H is 15%˜40% of totalheight of radiant section wall, most preferably, R varies in a range of3:7˜4:6, H is 20%˜40% of total height of radiant section wall.

[0042] In a pyrolysis furnace according to a preferred embodiment ofthis invention, said top burners and bottom burners can be used tosupply all heat need for high temperature cracking top burners andbottom burners may be, preferably combined oil-gas burners.

[0043] According to a form of modification of this invention, we canmaintain the heat supply ability of bottom burners constant, whileregulate the heat supply ability of top burners at a small range, so asto satisfy the requirement need for high temperature cracking ofdifferent kinds of feedstock.

[0044] According to a preferred embodiment of this invention, saidpyrolysis furnace can employ top burners and bottom burners of sameamount. The top or bottom burners may be arranged symmetrically aboutcenterline of top or bottom portion, the ratio of numbers of top/bottomburners is equal to, and corresponding to one another at top and bottomportions, moreover, the top/bottom burners heat supply ratio R can becontrolled by controlling the top/bottom burners fuel feeding ratio.

[0045] A pyrolysis furnace according to a preferred embodiment of thisinvention, wherein the used top burners and bottom burners may beburners of various kinds, as known to a person skilled in the art. Inorder to reduce cost, preferably employ conventional burners.

[0046] Because the top burners employ both liquid and gas fuels, or maybe an oil-gas combined burners, as compared with the wall burners heatsupply or bottom-wall combined heat supply manners, the presentinvention can reduce the number of burners, so as to reduce theinvestment and simplify the structure of pyrolysis furnace; moreover,the present invention can fully are the conventional burners, as top andbottom burners, which can be produced in our country, and isinexpensive, and simple in employ and maintenance.

[0047] Besides, due to employ of top and bottom burners combined heatsupply manner, the temperature distribution is relatively uniform, atthe same time the top/bottom burners heat supply ratio R can be adjustedin period of design according to the structure requirements, thus thedesign flexibility is greatly increased; in addition, employ of top andbottom burners combined heat supply manner of this invention, the outletof fuel gas of cross over section, which is located at top portion ofradiant section of traditional art, is shifted down to middle-upperportion of radiant section, this not bring about negative influence onthe cracking effect of pyrolysis furnace, but makes the height ofconvection section 2 to shift down, so that the overall height ofpyrolysis furnace may be lowered (by 3˜6 m in average, the particularheight is controlled by top/bottom burners heat supply ratio R). As aresult, the center of gravity of whole pyrolysis furnace is droppeddown, this reduce the capital construction cost. Moreover, in practicalemploy, according to the need for different outlet temperature ofvarious fuel kinds, it can maintain the heat supply ability of bottomburners as constant, as well as regulate the heat supply ability of topburners in a small range, to satisfy respective condition so as togreatly increase the flexibility in practical employ.

[0048] Here after, the present invention will be described in moredetail by way of examples, however, these examples are not intended torefer as limitations for this invention, For those skilled in the art,various changes and modifications can be made, depending the inspire,obtained from detailed description of present invention, for example,the pyrolysis furnace employing the radiant tubes arrangement manner ofthis invention, but the radiant tubes are back branched tubes; also forexample, pyrolysis furnace employing a common convection section for twoor more radiant sections. All these apparent changes are within thescope of the present invention.

EXAMPLE 1

[0049] A pyrolysis furnace has the yield of ethylene of 100 kiloton peryear. Said pyrolysis furnace comprising: a radiant section with furnacechamber height of about 17 m; a convection section shifted from radiantsection, with height about 15 m; a cross over section, horizontallyarranged and extended between said radiant and convection sections, theupper edge of outlet of crossover section is located about 6 m belowfrom the top portion of furnace chamber; 24 top burners, arrangedsymmetrically about the center line of top portion, and 24 bottomburners arranged symmetrically about the center line of bottom portion;multiple groups of convection tubes, horizontally arranged in convectionsection, and 48 groups of radiant tubes (type 2-1), vertically arrangedin radiant section. Because the location of crossover section is shifteddown about 6 m, the over all height of furnace is cut down about 6 m,where as the former pyrolysis furnace of the same scale, employing walland bottom burners combined heat supply manner need to comprise 24bottom burners and 48 wall burners.

[0050] If the furnace employ former staggered row arrangement of radianttubes, by only possibility is to arrange 48 groups of radiant tubes(type 2-1), the bends of adjacent groups and manifolds are located indifferent heights, as well as in different planes, the distance betweenis 1.8 times of outer diameter of radiant tubes, the length of offurnace chamber is about 20 m. In a reconstruction and innovationprogram design, the radiant tubes are arranged by the arrangement mannerof the present invention, all the first pass tubes are located at oneplane, all the second pass tubes are located at another plane, thedistance between two planes is 320 mm, when the distance between firstpass tubes is 2.4 times of outer diameter thereof, and the distancebetween second pass tubes is 3.5 times of outer diameter thereof, 64groups of radiant tubes (type 2-1) can be arranged in the same furnacechamber, this increases the productivity by 33%;

[0051] The radiant tubes are arranged by the arrangement manner of thepresent invention, when the distance between first pass tubes is 2.8times of outer diameter thereof, and the distance between second passtubes is 4.1 times of outer diameter thereof, 54 groups of radiant tubes(type 2-1) can be arranged in the same furnace chamber, this increasesthe productivity by 12.5%, at this time due to the distance betweenadjacent radiant tubes is increased, more uniform radiant conduction isobtained, this case is apparently advantageous for revamping oldfurnaces, and can remarkably increase productivity under condition ofminimum investment.

[0052] During high temperature cracking by means of said apparatus,controlling the top/bottom burners heat supply ratio R=3:7, thehydrocarbons feedstock and dilution steam mixture passes throughmulti-path convection tubes 1, horizontally extended in convectionsection 2, after recovering the heat of fuel gas in convection sectionand preheating to the temperature of crossover section, the hydrocarbons feedstock passes through the convection tubes 1 into cross tube5, after distributing an appropriate current by distributor, intoradiant tubes 7, vertically arranged in radiant section 3, the crackedproduct is heat exchanged in transfer line exchanger 4. The pyrolysisfurnace is fully based on the heat supplied by bottom burners 8 and topburners 9, and at same time the fuel gas, produced from top and bottomburners passes through the horizontally arranged crossover section 6,providing convection heat to convection section 2.

EXAMPLE 2

[0053] A pyrolysis furnace has the yield of ethylene of 60 kilo-ton peryear, said pyrolysis furnace comprising: a radiant section with furnacechamber height of about 14 m; a convection section, shifted from radiantsection, with height about 14 m; a crossover section, horizontallyarranged and extended between said radiant section and convectionsection; the upper edge of outlet of cross over section is located about3 m from top portion of furnace chamber; 24 top burners arrangedsymmetrically about the center line of top portion, and 24 bottomburners, arranged symmetrically about the center line of bottom portion;multiple groups of convection tubes, horizontally arranged in convectionsection, and 32 groups of radiant tubes (type 2-1), vertically arrangedin radiant section.

[0054] Because the location of cross over section is shift down about 3m, the overall length of furnace is cut down about 3 m, where as thepyrolysis furnace of the same scale, employing wall and bottom burnerscombined heat supply manner, need to comprise 24 bottom burners and 72wall burners.

[0055] The radiant tubes are arranged by former single row arrangement,the length of furnace chamber is about 15 m, the radiant tubes are twopass non-branched tubes (type 1-1), In order to avoid the mutual overlapradiant tubes bends and connected tubes in lower portion of furnacechamber, the distance between first pass tubes is 2.8 times of outerdiameter thereof, and the distance between second pass tubes is 2.3times of outer diameter thereof, in addition, it is a single rowarrangement, only 48 groups radiant tubes can be arranged. Inreconstruction design, the radiant tubes employ the arrangement mannerof the present invention, all the first pass tubes are located at oneplane, and all the second pass tubes are located at another plane, thedistance between two planes is 350 mm, when the distance between firstpass tubes is 2.8 times of outer diameter thereof, and the distancebetween second pass tubes is 2.3 times of outer diameter thereof, theradiant tubes employ the arrangement manner of the present invention,108 groups two pass non-branched tubes with different diameters (type1-1) can be arranged, this increases productivity to about 220%, at sametime, various radiant tubes have uniform heat conduction, in addition,the form and weight of bends in various groups and manifold are fullythe same, these components have high versatility, and all bends andconnected tubes are parallel arranged in lower portion of furnacechamber, without interference, and are simple for manufacture andmaintenance.

[0056] During high temperature cracking by means of said apparatus,controlling top/bottom burners heat supply ratio R=4:6, the hydrocarbonsfeed stock and dilution steam mixture passes through the multi-pathconvection tubes 1, horizontally extended in convection section 2, afterrecovering the heat of fuel gas in convection section, the hydro carbonsfeedstock passes through convection tubes 1 into cross tube 5, afterdistributing an appropriate current by distributor, passes into radianttubes 7, vertically arranged in radiant section 3. The pyrolysis furnaceis fully based on the heat, supplied by bottom burners 8 and top burners9, and at the same time, the fuel gas, produced from top and bottomburners passes through the horizontally arranged crossover section 6,providing convection heat to the convection section 2.

EXAMPLE 3

[0057] a pyrolysis furnace has the same pyrolysis furnace of example 1,but employing radiant tubes type 4-1. If single row of radiation tubesis employed, the distance between first pass tubes is about 1.8 times ofthe outer diameter thereof, the distance between second pass tubes isabout 1.4 times of the outer diameter thereof, in this case 32 groups ofradiant tubes can be arranged, instead, employing the arrangement mannerof radiant tubes of the present invention, the distance between firstpass tubes still maintain 1.8 times of the outer diameter thereof, butthe distance between second pass tubes is increased to 3.8 times of theouter diameter there of, all the first pass tubes are located at oneplane, all the second pass tubes are located at another plane, thedistance between two planes is 350 mm, This increases the productivityby about 50%. If the distance between first pass tubes enlarged to 2.4times of the outer diameter thereof, the distance between second passtubes enlarged to 5.1 times of outer diameter there of, and the distancebetween first and second pass tubes is 350 mm, in this case, 36 groupsof radiant tubes can be arranged, this increases the productivity byabout 12%, at this time, due to the enlargement of distance betweentubes, the ability for radiant convection by radiant tubes is far betterthan radiant tubes-employing single row arrangement.

What we claim is
 1. A pyrolysis furnace with new type radiant tubesarrangement, comprising: a) vertically arranged radiant section (3), inwhich burners and multiple groups of radiant tubes (7) are arranged forhigh temperature cracking hydrocarbons feedstock; b) vertically arrangedconvection section (2), located above the radiant section and axiallyshifted therewith, in said convection section multiple groups ofconvection tubes (1) are arranged for preheating the hydrocarbonsfeedstock; c) horizontally arranged crossover section (6), connectedbetween said radiant section (3) and said convection section (2);characterized in that, said multiple groups radiant tubes (7) are twopass tubes with different diameters, the first pass tubes and secondpass tubes in various groups are located at two parallel planes, and theprojection of each second pass tube is corresponding to the centerlocation of the projection connecting line, of the two first pass tubesadjacent therewith, the structure of each first pass tube and secondpass tube is the same.
 2. The pyrolysis furnace according to claim 1,wherein said radiant tubes (7) are type 2-1 of two pass branched tubeswith different diameters.
 3. The pyrolysis furnace according to claim 1,wherein said radiant tubes (7) are type 4-1 of two pass branched tubeswith different diameters.
 4. The pyrolysis furnace according to claim 1,wherein said radiant tubes. (7) are type 1-1 of two pass non-branchedtubes with different diameters.
 5. The pyrolysis furnace according toclaims 1-4, wherein the distance between two adjacent radiant tubes (7)is 1.8-6.0 times of outer diameter of radiant tubes at the same plane.6. The pyrolysis furnace according to claims 1-4, wherein the distancebetween two adjacent radiant tubes (7) is 1.8˜4.2 times of outerdiameter of radiant tubes at the same plane.
 7. The pyrolysis furnaceaccording to claims 1-4, wherein the distance between two adjacentradiant tubes (7) is 2.0˜2.8 times of outer diameter of radiant tubes atthe same plane.
 8. The pyrolysis furnace according to claims 1-4,wherein the distance between the planes where said first pass tubes andsecond pass tubes in every group of radiant tubes (7) are respectivelylocated is 100-600 mm.
 9. The pyrolysis furnace according to claims 1-4,wherein the distance between the planes where said first pass tubes andsecond pass tubes in every group of radiant tubes (7) are respectivelylocated is 200-500 mm.
 10. The pyrolysis furnace according to claims1-4, wherein the distance between the planes where said first pass tubesand second pass tubes in every group of radiant tubes (7) arerespectively located is 300-400 mm.
 11. The pyrolysis furnace accordingto claim 1, wherein bottom burners (8) and top burners (9) aresimultaneously arranged in said radiant section (3), more over, saidcrossover section (6) is extended out from a middle-upper portion ofsidewall of radiant section (3) and connected to bottom portion ofconvection section (2).
 12. The pyrolysis furnace according to claim 11,wherein the top wall of said cross over section (6) is located under thetop wall of said radiant section (3), its distance H is determined bythe top/bottom burners (9,8) heat supply ratio R, when R varies in arange of 1:9˜7:3, H is 10%˜50% of total height of radiant section (3).13. The pyrolysis furnace according to claim 11, wherein when R variesin a range of 2:8˜6:4, H is 10%˜40% of total height of radiant section(3).
 14. The pyrolysis furnace according to claim 11, wherein when Rvaries in a range of 2.5:7.5-5:5, H is 15%-40% of total height ofradiant section (3).
 15. The pyrolysis furnace according to claim 11,wherein when R varies in a range of 3:7˜4:6, H is 20%˜40% of totalheight of radiant section (3).
 16. The pyrolysis furnace according toclaim 11, wherein the number of said bottom burners (8) is equal to thenumber of said top burners (9), the top or bottom burners are arrangedsymmetrically about centerline of top or bottom portions andcorresponding to one another at top or bottom portion respectively. 17.A method of high temperature cracking hydrocarbons feedstock by means ofa pyrolysis furnace according to any one of claims 1-16, comprising: atconvection section (2), preheating the hydrocarbons feedstock in radianttubes (1), utilizing fuel gas of crossover section, came from radiantsection (3); at radiant section (3), high temperature cracking thepreheated hydrocarbons feedstock in radiant tubes (7), utilizing theheat supplied by top burners (9) and bottom burners (8); whereinmaintaining the heat supplied by bottom burners (8) constant, by meansof regulating the heat supplied by top burners (9) so as to satisfy thetemperature requirement for cracking different hydrocarbons feedstock.18. The use of pyrolysis furnace according to any one of claims 1-16 forhigh temperature cracking Hydrocarbons.